Finite Frequency Kernels for Ambient Noise Sources
Abstract
Ambient noise tomography and passive monitoring of Earth's crust promise a wealth of information and practical applications in many fields. However, there is increasing awareness that, in particular for observations of fundamental-mode surface waves in correlations, non-stationary and heterogeneously distributed ambient noise sources should be taken into account to avoid artifacts. While several techniques to do this have been proposed, there is to date no widely used manner in which ambient noise studies tackle this problem. We are developing a new method to invert for ambient noise sources while honoring realistic Earth structure. The first step was to devise a computational approach that enables us to model cross-correlation functions for arbitrary noise source distributions and to efficiently calculate noise source sensitivity kernels for 3-D heterogeneous Earth models. Using pre-computed correlation wavefields, we can iteratively update a noise source distribution model with little computational effort. While being applicable to 3-D Earth models, the tool we developed may equally be used to compute correlations and kernels from simpler, e.g. analytic, Green's functions. We have used this computational approach for a detailed analysis of source sensitivity kernels for the Earth's long-period background noise or 'hum'. In particular, our tests show that using a 3-D Earth model for the calculation of sensitivity kernels starts to result in subtle but recognizable differences, for the particular receiver geometries considered, at periods shorter than approx. 100 seconds. We also investigated the influence of multiple-orbit surface waves on hum source inversion. Their presence or absence has important implications for the sensitivity to noise sources. Our work is intended to establish the foundation of noise source inversions that account for the physics of wave propagation in the 3-D heterogeneous Earth, and to contribute to the future development of 'source-aware noise seismology'.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.S53C..01E
- Keywords:
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- 3384 Acoustic-gravity waves;
- ATMOSPHERIC PROCESSESDE: 0728 Ice shelves;
- CRYOSPHEREDE: 4560 Surface waves and tides;
- OCEANOGRAPHY: PHYSICALDE: 7255 Surface waves and free oscillations;
- SEISMOLOGY